1. Field of the Invention
The invention relates to portable test receivers for on-site functional testing of remote transmitters which monitor network power distribution transformers.
2. Description of the Related Art
The need for a remote monitoring capability of the operating conditions existing at individual transformers in an underground network power distribution system is well known in the art. Ideally, information such as 3 phase load currents on transformers, status of network protectors, oil temperatures of transformers in excess of specified limits, water levels, fuse status, and surrounding environment concerns such as vault access, air temperatures, etc. are required so that critical decisions can be made regarding network switching, problem analysis, peak load analysis, contingency studies, etc.
For example, the Remote Monitoring System, as manufactured by the Hazeltine Corporation, is typical of the current approach to meeting these requirements. The apparatus is a power line carrier system designed specifically to use network distribution feeders as the communication medium between network distribution transformers, located in underground vaults, and the substation. The system consists of a transmitter and sensors installed at the distribution transformer to be monitored and a receiver located at the network substation. The sensors provide input data, such as transformer load currents and network protector position, to the transmitter, which periodically transmits the information, including vault identification, by power line carrier signal over the distribution feeder to the substation receiver. Coupling of the signal to the feeder is accomplished by direct connection to the low voltage side of the network distribution transformer. At the substation, the signal is magnetically detected from the feeder by means of a pick-up coil attached to the feeder cable. Direct electrical connection to the feeder is not required. The substation receiver decodes the signal information and stores the data for presentation on demand. The receiver is microprocessor controlled. In addition to cross referencing data to the actual vault identification, the receiver produces the data in numerous "by exception" formats controlled by command inputs. In a particular situation, such as backfeed location, only the data of interest is presented for analysis. Network protector status and transformer loading prior to and following feeder outages, are available, thereby reducing the need for feeder patrols. Peak period transformer loading data is instantly available for the whole network simultaneously for more accurate planning than was previously possible with manual measurements, which are not concurrent. Monitoring of spot networks, local areas, and critcal locations for maintenance work can be achieved remotely without the need for field crews on-site to check status.
While such systems have proven to be extremely reliable and produce costs savings only achievable with a real-time monitoring system, the transmitters of the monitoring system require that they be periodically checked to ensure that they are operating properly. It is also important to confirm the message and frequency being transmitted. Ideally, this should be done using a device that can be easily transported to the various field locations to test the functioning of the remote monitoring transmitters.
A portable test receiver designed for the specific purpose of decoding the transmitted signal of a remote transmitter that is monitoring the status of an underground transformer, thereby functioning as a field troubleshooting device, must be small, lightweight, battery powered and relatively inexpensive. Prior art receivers are unable to meet these specifications.